Project Summary The acute respiratory distress syndrome (ARDS) is a deadly condition characterized by the rapid onset of hypoxemia and respiratory failure. The mainstay of therapy for ARDS patients is supportive care with mechanical ventilation (MV). Although life-saving, mechanical ventilation can exacerbate existing lung injury and even cause de novo injury, known as ventilator induced lung injury (VILI). VILI arises from mechanical forces during MV including excessive stretch (volutrauma), excessive pressure (barotrauma), and injury due to repeated collapse and reopening of lung units (atelectrauma). The molecular mechanisms by which these mechanical forces propagate lung injury remain poorly understood. Clinicians try to prevent VILI by monitoring airway pressures and using low tidal volumes, but injury can persist even when these parameters are in a ?safe? range. Currently, there are no pharmacologic therapies to prevent or treat VILI in patients with ARDS. mTORC1 is a central regulator of cell growth and lipid metabolism. In contrast to canonical activation of mTORC1 under favorable growth conditions, we recently discovered that mTORC1 is activated in lung epithelial cells following injurious mechanical ventilation. Furthermore, we also found that pharmacologic mTORC1 inhibition prevents lung injury during mechanical ventilation. We hypothesize that mTORC1 activation plays a central role in mediating VILI and represents a novel therapeutic target in ARDS. We will determine the mechanisms by which mTORC1 inhibition prevents VILI using mice with mTORC1 inactivation in type I and type II alveolar epithelial cells as well as novel in vitro models of mechanical ventilation in the human lung. In Aim 1 we will identify how mTORC1 activation induces surfactant dysfunction during ventilator induced lung injury. In Aim 2 we will identify the mechanisms by which mTORC1 regulates epithelial membrane repair following injurious mechanical ventilation. In Aim 3 we will use clinically relevant 2-hit models that utilize mechanical ventilation following lung injury from sepsis or influenza pneumonia to test the efficacy of mTORC1 inhibition to prevent VILI in ARDS. Our studies will provide an in-depth understanding of how mTORC1 activation impairs surfactant function and membrane repair during VILI and will identify novel drug targets for patients with ARDS.